1. Field of the Invention
The invention relates to a conductivity sensor with a substantially circularly cylindrical casing of synthetic material and with metal measuring electrodes in its planar, substantially circular front wall, of which at least two voltage electrodes and at least two current electrodes form poles.
2. Description of the Related Art
Such known conductivity sensors entail the problem that they project into the reaction vessels and thus hinder the cleaning operation, which is especially critical in the case of pharmaceutical agents. In addition, they cannot be used, for example, in a thawing vessel filled with floating, ice chips, since they might be damaged. In fiber-containing media, the known sensors become clogged and can therefore not be used at all or only with special cleaning devices. This leads to a considerable technical expenditure and thus to an increase in costs. Furthermore, using the known conductivity sensors impairs the flow of the media current into which they project.
It is an object of the present invention to provide a conductivity sensor of the above described type which has low structural expenditure, avoids the cited disadvantages and yet has satisfactory sensitivity.
This task is solved in a conductivity sensor of the above described type by encompassing the at least two substantially circular voltage electrodes with at least two plane-form current electrodes extending substantially in a semicircle or by at least four current electrodes substantially circular and disposed in two semicircles.
Consequently, the invention provides an entirely novel measuring electrode configuration as a solution to the problems associated with the prior art. In spite of smaller cross sectional dimensions, a large measuring range of up to 850 milli Siemens (mS) can be covered such that application in the most diverse installations is possible. Due to the nearly planar surface of the front wall, the conductivity sensor according to the invention can be readily cleaned and is immune to contamination. It is, moreover, mechanically extraordinarily rugged. The interconnection can take place as four-pole or a two-pole conductivity sensor. In the configuration of individual circular current electrodes in two semicircles about the voltage electrodes, a closer approximation takes place to two plane-form current electrodes, substantially extending in a semicircle, the more poles are used. The number of measuring electrodes can also be varied in order to attain adaptation to special conditions. In the special configuration of the invention, the electrodes the measuring electrode area is markedly smaller than in conventional conductivity sensors and the voltage electrodes disposed on the inside are integrated better into the measuring field. The conductivity sensor according to the invention further has no beam shadow and can therefore also be used in fermenters which are equipped with CIP (Cleaning in Process).
In a special embodiment of the invention, two voltage electrodes are disposed at a distance from one another, and one of the two voltage electrodes has a nearly semicircularly encircling current electrode associated therewith.
The voltage electrodes and the semicircularly extending current electrodes mirror one another, wherein they are preferably symmetrically disposed on one and the same diameter of the front wall.
According to a further preferred embodiment of four or six substantially circular current electrodes, two or three of the substantially circular current electrodes are in a semicircular configuration about two voltage electrodes disposed at a distance from one another.
The substantially circular voltage electrodes are therein preferably disposed on a diameter of the front wall and the four or six current electrodes are preferably disposed on, or mirror-symmetrically with respect to, this diameter.
A further characteristic of the invention is that the temperature sensor is built into one of the measuring electrodes itself.
If the casing comprises an insulating synthetic material, such as polyether ether ketone (PEEK), glass or a comparably resistant insulator, and the measuring electrodes comprise special steel, tantalum, Hastelloy (a nickel-molybdenum-iron alloy known by this trademark), artificial carbon or like conductors resistant to liquids, the conductivity sensor conforms to FDA standards. In addition, its use up to 200xc2x0 C. is possible and chemical resistivity is ensured, such that application in many fields under chemical and physical load is possible. Furthermore, all of the materials can be autoclaved up to at least 140xc2x0 C.
Further, due to its small diameter, the casing can fit into a 25 mm connection socket such that the application on many fermenters can take place without requiring enclosures.
With a short installation length of less than approximately 10 mm, the danger of damage and interference with the media current is only minimal.
Further objectives, characteristics, advantages and application feasibilities of the invention are evident based on the following description of embodiment examples in conjunction with the drawing. All described and/or graphically depicted characteristics by themselves or in any combination form the subject matter of the invention independently of their recapitulation in individual claims or their reference back.